Carboxymethyl chitosan/poly (ethylene oxide) (CCTS/PEO) composite is firstly reported as a water soluble binder for the application of 5 V LiNi0.5Mn1.5O4 cathode in Li-ion batteries. Both CCTS and PEO show a high electrochemical oxidation potential of above 5.0 V (vs. Li/Li+). The electrochemical performances of LiNi0.5Mn1.5O4 (LNMO) cathodes with CCTS/PEO composite binders of different mass rates are investigated, it is found that LiNi0.5Mn1.5O4 cathode with an optimized CCTS/PEO (85/15, w/w) composite exhibits a slightly better cycling performance than that of polyvinylidene fluoride (PVDF), retaining 81.4% capacity as compared with 79.8% for PVDF at 0.5C rate after 200 cycles. LNMO with PEO/CCTS (85/15, w/w) exhibited the better rate capability than that of PVDF. These results demonstrate that CCTS/PEO composite can be potentially used as a water-soluble binder for 5 V LNMO cathode. (C) 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.